The preparation of activated carbons (AC-HxPyOz) by four kinds of oxyacids of phosphorus (H3PO4, H4P2O7, HPO3 and H3PO3) activation of lotus stalk (LS) was studied, with a particular focus on the effect of these HxPyOz on both surface chemistry and porous texture. The XRD analysis of the samples after HxPyOz impregnation showed H4P2O7 had the strongest influence on the crystallinity of LS. Thermo gravimetric studies of the pyrolysis of LS-HxPyOz indicated that these HxPyOz had a very different influence on the thermal degradation of LS. The prepared activated carbons were characterized by SEM, N-2 sorption/desorption isotherms, XRD, FTIR and Boehm's titration. Batched sorption studies were performed to compare adsorptive properties of the carbons toward trimethoprim (TMP). The surface area and pore volume of AC-H3PO4 and AC-H4P2O7 were much higher than AC-HPO3 and AC-H3PO3. Boehm's titration results indicated that AC-H4P2O7 and AC-H3PO3 possessed more acidic oxygen functionalities than AC-H3PO4 and AC-HPO3. The structure of the AC-HPO3 was kept as its starting material after activation. Activation with H3PO3 would result in the aromatization of the carbon. The sorption affinities of TMP follows an order of AC-H4P2O7 > AC-H3PO4 > AC-H3PO3 > AC-HPO3. (C) 2012 Elsevier B.V. All rights reserved.